Safety device



N. B. LUND SAFETY DEVICE Oct. 17, 1933.

Filed June 1, 1929 INVENTOR NELS B.LUN

Patented Oct. 17, 1933 PATENT OFFICE v 1,931,232 SAFETY DEVICE Nels B. Lund, Seaford, N. Y., assignor, by mesne assignments, to The Dorr Company, Inc., New York, N. Y., a corporation of Delaware Application June 1, 1929. Serial No. 367,784

1 Claim. (Cl. 192116.5)

This invention relates to overload safety devices and more particularly to devices of this kind which are adapted for use with sedimentation apparatus, such as thickeners of the Dorr type. I

In the thickeners to which this invention is particularly applicable, a rotary rake structure acting to transfer the sludge at the bottom of a tank to acentral outlet, is mounted on a vertical shaft which is rotated by means of a worm gear mounted thereon and a worm meshing with said worm gear. The moving parts of this apparatus are designed to move only a certain maximum amount of settled solids having a predetermined resistance to the rake mechanism; and it sometimes occurs that due, for example, to excessive feed, changes in the character of the solids, or changes in the proportion of solids in the feed, or for more than one of these conditions, the settled solids build up to such an extent that the resistance offered to the raking vmechanism is above that for which the mechanism was designed and tends to warp and break the mechanism. Such difficulties may also arise from obstruction of the rakes by foreign obiects, such as tools, dropped into the tank.

Heretofore such thickeners have been pro vided with devices responsive to increase of thrust of the worm above a predetermined point (due to excessive resistance to the rake action) to signal the operator that excessive resistance to operation is being experienced by the raking mechanism. If, however, the operator is not present, or ifhe fails to act promptly upon operation of the signal, there is danger of breakage of the apparatus.

The main object of the invention is to provide means for preventing damage under such conditions. throwing off the power when such conditions arise.

Other objects and advantages of the invention will appear upon consideration of the following description and the accompanying drawing, in which:

Fig. 1 is a view in front elevation illustrating a preferred embodiment of the invention;

Fig. 2 is a sectional plan View taken along the line 2-2 of Fig. 1, certain parts being omitted; and

Fig. 3 is a detail sectional view taken along the line 3--3 of Fig. 1.

The objects of the invention are attained by providing an alarm, a quick acting device for shutting ofithe power and means for operating in the direction of the arrow 12 (Fig. 1).

Another object relates to means for said alarm upon overload reaching a noticeable degree and for operating said quick acting device to shut 01f the power upon increase of overload to a dangerous degree. In its preferred form the invention is embodied in a construction in which the shaft of a driving worm is yieldably supported against the thrust resulting from operation and serves to move an indicator in accordance with the degree of such thrust. Upon movement of the indicator to a predetermined position an alarm circuit is closed to operate a suitable alarm and the alarm circuit is maintained in closed condition until the overload is decreased sufficiently to permit the indicator to. move back of said position, or is thrown off in some other way. If, however, the overload increases past a danger point corresponding to a predetermined position of the indicator, a quick action, throw off switch in the circuit of a motor for operating the apparatus is opened and'the apparatus is stopped.

Referring to the drawing, the worm 10, through which the worm wheel (not shown) connected with the rake structure is driven, is rotated in the direction indicated. by the arrow 11 (Fig. 1) and, in driving the worm wheel, is subjected to a thrust The worm 10 is fixed on a shaft 13 of which the end toward which the thrust acts enters an opening in the worm gear bracket 14, and the thrust is transmitted through a thrust ball bearing 15, mounted on a reduced portion of the shaft 13 to a member 16 having a reduced portion entering said opening in the Worm gear bracket and engaging said ball bearing, and a broader. portion mounted on tubular spacers 17 surrounding rods or bolts 18 secured at their inner ends to the worm gear bracket 14 and passing at their outer ends through a head 19 in the form of a plate which is held against said spacers 17 by suitable means, such as nuts. Interposed between the head 19 and the member 16 is a thrust spring 20 which is of sufficient strength to hold the member 16 to movement within a relatively small range under normal load conditions.

Secured to an upright part of the Worm gear bracket 14 are a bracket 21 in the form of a loop, supporting a switch 22 (which may, for example, be the General Electric safety switch type FP-15 oil circuit breaker, 3 pole single throw), and a bracket 23 having its lower end secured in the end of the loop of the bracket 21 adjacent to said upright part of the worm gear bracket 14. Said lower end of the bracket 23 includes a yoke portion 24 extending horizontally away from the bracket 14 and receiving the lower part of a pointer mounted to swing in a vertical plane about the axis of a pivot 23 extending across the opening in said yoke 24 and supported in the sides thereof, the pointer being provided at its lower end with a set screw 2'1 which under normal working conditions is held in engagement with the thrust member 16. The set screw 27 is threaded through the split lower end of the pointer and the pressure on the set screw 2'? may be regulated by means, such as a screw or bolt 28. The screw 27 is maintained in contact with the member or,

bracket spring head 16 by means including an eye bolt 29 connected with the pointer 25 by means of a pivot or pin 30 passing through the eye oi the bolt and secured in the pointer. The shank of the bolt passes through an opening in the yoke 24 and the eye bolt is urged outwardly through said opening by means of a spring 31 interposed between the yoke 24 and a cup washer 32 held on the shank of the eye bolt by suitable means such as nuts threaded on the end of said shank.

Extending upwardly from one side oi! the yoke 24 is an index bracket 33 having its upper end extended parallel to the path of the upper end of the pointer and in correspondence with the range of movement thereoi, and this bracket is utilized to hold suitable means, such as a card, to receive a record of the range of movement of the upper end of the pointer, by means of a pencil held in a pencil holder 34 on the pointer 25. The pointer 25-also carries a spring contact 35 adjustably scoured thereto by means of a screw passing thl'bugl'i a slot in the contact and threaded into the pointer, and this contact 35 is so adiusted that. when the pointer is swung beyond its limit for normal load conditions (said limit being indicated by the dot-and-dash line 36 on Fig. 1), it will engage a stationary spring contact 37 mounted on a member 38 of insulating material secured to the bracket 23, and will close a circuit 39 conneotedwith a suitable source of power, such as a battery 40, and including a bell 41, or other signal, the circuit being completed through a ground.

Upon operation of the bell 41, an attendant should investigate immediately to avoid damage to the apparatus and to remedy the condition causing the overload. If, however, the attendant did not hear the signal or he did not attend to the apparatus quickly enough, there would be great danger or damage thereto, and for this reason there should be provided means for stopplug the apparatus when the overload becomes dangerously high. To this end the pointer 25 is connected by a suitable flexible connector, such as a chain 42, with the control handle 43 of the throw off switch 22 which is connected with the motor (not shown) by conductors 44 enclosed in suitable conduits 45. The chain 42 is so connected with the pointer 25 and with the control handle 43 and of such length that the switch 22 will be thrown off when the pointer 25 reaches the position indicated by the dot-and-dash line 46 and which is reached only when the overload becomes dangerous.

In recapitulation, the operation of the safety device is substantially as follows: Ordinarily the pointer 25 will not reach the position, indicated by the line 36, but, when it reaches this position or moves slightly beyond the same, the signal is sounded. This condition may be remedied without attention and under such circumstances the pointer will return to its normal range of movement and the signal will be silenced. If, however, the overload continues without reaching the danger point indicated by the dot-and-dash line 45, the signal bell 41 will continue to ring but there will be no other action by the safety device. In the event that the overload increases until the pointer passes the limit indicated by the line 46, the handle 43 will be shifted and the apparatus stopped. Upon relief from such overload the pointer 25 will return to its normal position, but the control handle 43 will have to be restored manually to its position for closing the motor circuit.

It should be understood that various changes may be made in the construction and arrangement of parts without departing from the true spirit and scope of the invention.

Having thus described my invention, I claim:

Apparatus oi the class described comprising a drive element, means moved laterally by said drive element when abnormal resistance is encountered by said drive element, a motor circuit 115 for said drive element, a switch for controlling said motor circuit, a pivoted pointer arm rotated by motion of said laterally movable means, a flexible connection between said pointer arm and said switch whereby rotation of said pointer arm 120 past a predetermined point will act upon said switch to open it, an alarm circuit, a contact carried by said pointer arm, and means for adjusting the point of making and breaking of said alarm circuit by said contact whereby when said pointer arm opens said switch said contact will substantially simultaneously complete said alarm circuit.

NELS B. LUND. 

